apt-get install fglrx-driver fglrx-kernel-src

read README: /usr/share/doc/fglrx-kernel-src/README.Debian.gz
and do as metioned in this README.

dpkg -i fglrx-kernel-2.6.xxxxxx.deb

aticonfig –initial=dual-head –dtop=clone –resolution=1024×768,800×600 –mode2=1024×768,800×600 –force-monitor=crt1,crt2